1. Field of the Invention
The present invention generally relates to a patient interface device for use in a pressure support system that supplies a flow of gas to the airway of a patient, and, in particular to a patient interface device that includes dual-cushion support and to a pressure support system that includes such a patient interface device.
2. Description of the Related Art
There are numerous situations where it is necessary or desirable to deliver a flow of breathing gas non-invasively to the airway of a patient, i.e., without intubating the patient or surgically inserting a tracheal tube in their esophagus. For example, it is known to ventilate a patient using a technique known as non-invasive ventilation (NIV). It is also known to deliver continuous positive airway pressure (CPAP) or variable airway pressure, such as a bi-level pressure that varies with the patient's respiratory cycle or an auto-titrating pressure that varies with the monitored condition of the patient. Typical pressure support therapies are provided to treat a medical disorder, such as sleep apnea syndrome, in particular, obstructive sleep apnea (OSA), chronic obstructive pulmonary disease (COPD), or congestive heart failure (CHF).
Non-invasive ventilation and pressure support therapies involve the placement of a patient interface device, which is typically a nasal or nasal/oral mask, on the face of a patient to interface the ventilator or pressure support system with the airway of the patient so that a flow of breathing gas can be delivered from the pressure/flow generating device to the airway of the patient. It is known to maintain such masks on the face of a patient by a headgear having upper and lower straps, each having opposite ends threaded through connecting elements provided on the opposite sides and top of a mask.
Typically patient interface devices include a mask shell having a cushion attached to the shell that contacts the surface of the patient. The mask shell and cushion are held in place by a headgear that wraps around the head of the patient. The mask and headgear form the patient interface assembly. A typical headgear includes flexible, adjustable straps that extend from the mask to attach the mask to the patient.
Because such masks are typically worn for an extended period of time, a variety of concerns must be taken into consideration. For example, in providing CPAP to treat OSA, the patient normally wears the patient interface device all night long while he or she sleeps. One concern in such a situation is that the patient interface device is as comfortable as possible, otherwise the patient may avoid wearing the interface device, defeating the purpose of the prescribed pressure support therapy. It is also important that the interface device provide a tight enough seal against a patient's face without discomfort. A problem arises in that in order for the mask to maintain a seal without any undue gas leaks around the periphery of the mask, the mask may be compressed against the patient's face.
Many patient interface devices have been developed that attempt to balance the competing interests of patient comfort versus minimizing leakage. In addressing this issue, many patient interface devices have focused on the design of the cushion. Early cushion designs were typically a flap of material or a balloon, i.e., air-filled cushion, that contacted the face of the user. Further design developments include contouring the patient contacting portion of the cushion and/or making the seal customizable to the surface or underlying tissues of the user. Still further cushions have employed multiple flaps so that the outermost flap provides a sealing function. See, e.g., U.S. Pat. No. 4,791,051 to Toffolon.
Although these conventional patient interface devices have advanced the art, the need still exists for a patient interface device that improves upon existing devices, for example, to maximize patient comfort while minimizing leak, during delivery of a positive airway pressure or flow of gas to the airway of the user. For example, many conventional patient interface devices tend to focus the strapping force applied on the patient to a relative small area of the patient's face around the nose, mouth, or both. Existing patient interfaces also may not provide a stable platform that supports the cushion on the patient's face.